Pass FlatViewGroup to DrawCommand.draw()

Summary: @public To render `View`s inside `FlatViewGroup`, we need to pass the parent to `DrawCommand.draw()` method. Used in a followup diff.

Reviewed By: sriramramani

Differential Revision: D2564478

ReactAndroid/src/main/java/com/facebook/react/flat/DrawCommand.java

@@ -25,5 +25,5 @@ public interface DrawCommand {
    *
    * @param canvas The canvas to draw into
    */
-  public void draw(Canvas canvas);
+  public void draw(FlatViewGroup parent, Canvas canvas);
 }